Taking advantage of what you're doing, I think it's worth considering the export time of the geometry at the time of rendering.

Now we're using increasingly denser models for archviz, with more realistic trees and grass with more detail. Recently I did the some tests and unfortunately with the current version the process is slow. Speaking with the developers of the Appleseed plugin, I have been told that this is because of blender, because it limits this task to the use of python.

It seems that the only option is to get an own version of blender with the integrated plugin, as the people of Octane and Vray have done.

From what previous YafaRay developers told me, that's exactly what was done with the old YafRay. It was integrated into Blender directly. However they told me it was a software maintenance nightmare.

I fully agree that Blender's Python API is somewhat slow and does not give us too much control on things, but I'm working on a better way to interact with YafaRay, improving the current YafaRay API to allow for a more interactive API. I'm not sure yet but I hope to get a little bit better speed on the Blender exporting process.

Something I noticed very clearly is that any operation in Python is a lot slower that doing the same operation in C++. Therefore I will try to find out what time-critical parts of the Blender Exporter can (if at all) be moved into the Core C++ code to speed things up.